Catalysts and methods for alcohol dehydration

ABSTRACT

Provided is a process for preparing a diaryl ether compound through the dehydration of an aromatic alcohol compound in the presence of a dehydration catalyst. The dehydration catalyst is an oxide of a heavy rare earth element, wherein the heavy rare earth element is terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, or mixtures thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from provisional application Ser. No.61/653,494, filed May 31, 2012, which is incorporated herein byreference in its entirety.

BACKGROUND

This invention relates generally to catalysts and methods for thedehydration of aromatic alcohol compounds to ethers. More particularly,the invention uses a dehydration catalyst comprising an oxide of a heavyrare earth element for the dehydration of aromatic alcohol compounds todiaryl ethers.

Diaryl ethers are an important class of industrial materials. Diphenyloxide (DPO), for instance, has many uses, most notably as the majorcomponent of the eutectic mixture of DPO and biphenyl, which is thestandard heat transfer fluid for the concentrating solar power (CSP)industry. With the current boom in CSP has come a tightening of thesupply of DPO globally and questions surrounding the sustainability ofthe technology have arisen.

Diaryl ethers are currently manufactured commercially via two majorroutes: reaction of a haloaryl compound with an aryl alcohol; orgas-phase dehydration of an aryl alcohol. The first route, for examplewhere chlorobenzene reacts with phenol in the presence of caustic and acopper catalyst, typically leads to less pure product and requires highpressure (5000 psig), uses an expensive alloy reactor and producesstoichiometric quantities of sodium chloride.

The second route, which is a more desirable approach, accounts for thelargest volume of diaryl ethers produced but requires a very active andselective catalytic material. For instance, DPO can be manufactured bythe gas-phase dehydration of phenol over a thorium oxide (thoria)catalyst (e.g., U.S. Pat. No. 5,925,798). A major drawback of thoriahowever is its radioactive nature, which makes its handling difficultand potentially costly. Furthermore, the supply of thoria globally hasbeen largely unavailable in recent years putting at risk existing DPOmanufacturers utilizing this technology. Additionally, other catalystsfor the gas-phase dehydration of phenol, such as zeolite catalysts,titanium oxide, zirconium oxide and tungsten oxide, generally sufferfrom lower activity, significantly higher impurity content and fastcatalyst deactivation.

With a chronic shortage of diaryl ethers such as DPO in sight and apressing need to increase capacity, it has become crucial to developalternate methods to produce such materials in a cost-effective andsustainable manner.

The problem addressed by this invention, therefore, is the provision ofnew catalysts and methods for manufacture of diaryl ethers from arylalcohol compounds.

STATEMENT OF INVENTION

We have now found that a catalyst comprising an oxide of a heavy rareearth element is effective for the preparation of diaryl ethers fromaromatic alcohol compounds. Advantageously, the catalyst exhibitsremarkable selectivity for the desired product. Moreover, the catalystis non-radioactive. This invention, therefore, represents a uniquesolution for diaryl ether supply issues globally.

In one aspect, there is provided a method for preparing a diaryl ether,the method comprising dehydrating an aromatic alcohol compound over adehydration catalyst, wherein the dehydration catalyst is an oxide of aheavy rare earth element.

In another aspect, there is provided a method for producing a heattransfer fluid, the method comprising: preparing a diaryl ether bycontacting an aromatic alcohol compound with a dehydration catalyst,wherein the dehydration catalyst is an oxide of a heavy rare earthelement; isolating the diaryl ether from the dehydration catalyst; andmixing the isolated diaryl ether with biphenyl, wherein the mixtureforms a eutectic mixture.

DETAILED DESCRIPTION

Unless otherwise indicated, numeric ranges, for instance as in “from 2to 10,” are inclusive of the numbers defining the range (e.g., 2 and10).

Unless otherwise indicated, ratios, percentages, parts, and the like areby weight.

As noted above, in one aspect the invention provides a method forproducing a diaryl ether by dehydrating an aromatic alcohol compoundover an oxide of a heavy rare earth element. It has been discovered thatsuch catalysts exhibit high selectivity for the desired diaryl ethercompounds with relatively low formation of undesirable byproducts. Forinstance, as demonstrated by the examples, in the synthesis of diphenyloxide from phenol, a selectivity for the DPO of 50% or greater may beachieved. In some embodiments, a selectivity of 80% or greater may beachieved. In some embodiments, a selectivity of 90% or greater, oralternatively 95% or greater is possible.

In addition to being highly selective, the catalysts are furtheradvantaged because they are non-radioactive, thus eliminating the safetyand environmental issues, as well as higher costs, associated with thehandling of radioactive materials, such as the thoria catalysts of theprior art.

The dehydration catalyst of the invention comprises an oxide of a heavyrare earth element. By a “heavy rare earth element” is meant terbium,dysprosium, holmium, erbium, thulium, ytterbium, lutetium, or mixturesthereof. By “oxide of heavy rare earth element” is meant a compound thatcontains at least one oxygen-heavy rare earth element bond. Examplesinclude, but are not limited to, Tb₂O₃, Tb₄O₇, TbO₂, Tb₆O₁₁,Dy₂O₃,Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃, and Lu₂O₃.

In some embodiments, the catalyst is an oxide of terbium. In someembodiments, the catalyst is an oxide of dysprosium In some embodiments,the catalyst is an oxide of holmium. In some embodiments, the catalystis an oxide of erbium. In some embodiments, the catalyst is an oxide ofthulium. In some embodiments, the catalyst is an oxide of ytterbium. Insome embodiments, the catalyst is an oxide of lutetium. Mixtures ofoxides, such as mixtures of oxides of one heavy rare earth element, ormixtures of oxides of two or more different heavy rare earth elements,are also encompassed by the invention.

The catalyst may optionally contain other atoms, such as halogens,including chloride or fluoride. In some embodiments, a preferredcatalyst for use in the invention contains a heavy rare earth element,oxygen and chlorine atoms. In some embodiments, the catalyst comprises,in addition to the heavy rare earth element and oxygen, chlorine in anamount of less than 40 weight percent, alternatively 30 weight percentor less, alternatively 17 weight percent or less, alternatively 10weight percent or less, or alternatively 2 weight percent or less. Insome embodiments, the catalyst comprises the chlorine in an amount of atleast 0.001 weight percent, alternatively at least 0.1 weight percent,alternatively at least 1 weight percent, or alternatively at least 2weight percent. In some embodiments, the catalyst contains between 1 and17 weight percent chlorine. The chlorine is in the form of chloride ion(Cl⁻). Non limiting examples of suitable compounds may include terbiumoxychloride, dysprosium oxychloride, holmium oxychloride, erbiumoxychloride, thulium oxychloride, ytterbium oxychloride, lutetiumoxychloride, or an oxide of the heavy rare earth element also containinga chloride (e.g., from NH₄Cl, HCl, etc., or from chloride containingheavy rare earth element precursors). By “oxychloride” is meant acompound that contains metal-oxygen and metal-chlorine bonds. Examplesfurther include, again without limitation, heavy rare earth elementoxide catalysts based on chlorate oxyanions, such as hypochlorite(ClO⁻); chlorite (ClO₂ ⁻); chlorate (ClO₃ ⁻), perchlorate (ClO₄ ⁻) whereCl is oxidized (+2, +3, +4, +5), as well as amorphous materials.

Catalysts suitable for use in the invention may be prepared by thoseskilled in the art or they may be purchased from commercial vendors.

The catalyst may optionally contain a binder and/or matrix material thatis different from the active oxide of the heavy rare earth element.Non-limiting examples of binders that are useful alone or in combinationinclude various types of hydrated alumina, silicas and/or otherinorganic oxide sols, and carbon. Upon heating, the inorganic oxide sol,preferably having a low viscosity, is converted into an inorganic oxidebinder component.

Where the catalyst composition contains a matrix material, this ispreferably different from the active catalyst and any binder.Non-limiting examples of matrix materials include clays or clay-typecompositions.

The catalyst, including any binder or matrix materials, may beunsupported or supported. Non-limiting examples of suitable supportmaterials include titania, alumina, zirconia, silica, carbons, zeolites,magnesium oxide, and mixtures thereof. Where the catalyst contains abinder, matrix or support material, the amount of oxide of heavy rareearth element (the active component of the catalyst) may be between 1and 99 percent by weight based on the total weight of the catalyst(including the oxide, and any support, binder or matrix materials).

The catalyst may be formed into various shapes and sizes for ease ofhandling. For instance, the catalyst (plus any binder, matrix, orsupport) may be in the form of pellets, spheres, or other shapes used inthe industry.

Aromatic alcohol compounds suitable for use in the process of thisinvention include aromatic compounds containing at least one alcoholgroup and one, two, three or more aromatic moieties. Suitable compoundsinclude phenols and α- and β-hydroxy-substituted fused aromatic ringsystems. Apart from the hydroxy substituent, the compounds may beunsubstituted, as in phenol or naphthol. Optionally, however, thecompounds may be further substituted with at least one alkyl groupcontaining from 1 to about 10 carbon atoms, preferably, from 1 to 3carbon atoms, or substituted with at least one alternative substituentwhich is inert to the dehydration coupling reaction. Suitable inertsubstituents include cyano, amino, nitro, carboxylic acid (e.g.,C₀-C₆—COOH), ester, C₆-C₁₂ aryl, C₂-C₆ alkenyl, alkyloxy, aryloxy, andphenoxy moieties. It is also possible for the aromatic alcohol compoundto be substituted with both an alkyl substituent and one of thealternative inert substituents. Each of the aforementioned alkylsubstituents and/or alternative inert substituents is attachedpreferably to an aromatic ring carbon atom which is located in an ortho,meta or para position relative to the hydroxy moiety. Optionally, thealkyl substituent may contain from 3 to 4 carbon atoms, and incombination with a phenol or fused aromatic ring system may form asaturated ring fused to the aromatic ring. An acceptable feed maycontain a mixture of aromatic alcohols, including mixtures of theforegoing.

Non-limiting examples of suitable phenols include unsubstituted phenol,m-cresol, p-cresol, 3,4-xylenol, 3,5-xylenol, and 3,4,5-trimethylphenol.Other suitable phenols include compounds corresponding to theabove-mentioned examples except that one or more of the methylsubstituents are replaced by an ethyl, propyl or butyl substituent.Non-limiting examples of α- and β-hydroxy-substituted fused aromaticring systems include α- and β-naphthol and 5-tetralinol. Othernon-limiting examples of aromatic alcohols include benzenediols(catechol, resorcinol or hydroquinone), o-cresol, o-phenylphenol,m-phenylphenol or p-phenylphenol. One skilled in the art may find otherphenols and α- and β-hydroxy-substituted fused aromatic ring systemswhich are also suitable for the purposes of this invention. Preferably,the aromatic alcohol is unsubstituted phenol or a substituted phenolwherein the substituent is methyl, ethyl or hydroxyl. More preferably,the aromatic alcohol is unsubstituted phenol, cresol or a benzenediol.Most preferably, the aromatic alcohol is unsubstituted phenol.

According to the method of the invention for preparing a diaryl ether, adehydration catalyst as described herein is contacted with the aromaticalcohol compound. The contacting of the catalyst with the aromaticalcohol compound is carried out under reaction conditions such that thediaryl ether is formed.

The catalyst is contacted with the aromatic alcohol compound either inthe gas phase or in the liquid phase. In addition, the aromatic alcoholmay be diluted with a diluent or it may be neat. Suitable diluentsinclude, without limitation, nitrogen, argon, water vapor, water, oxygenor hydrogen. When a diluent is used, the concentration of the aromaticalcohol compound may be, for instance, 1 volume percent or greater andless than 100 volume percent.

In a preferred embodiment, the aromatic alcohol is contacted with thecatalyst in the gas phase. Typically, the aromatic alcohol is introducedinto a reactor containing the catalyst at elevated temperature, forinstance, between 200 and 800° C., alternatively between 300 and 600°C., alternatively between 400 and 600° C., or alternatively between 450and 550° C. The reaction may be conducted at atmospheric pressure, underreduced pressure, or at elevated pressure such as up to 5000 psi. Insome embodiments, atmospheric pressure or slightly above (e.g., up toabout 50 psi) is preferred. In some embodiments, the gas flow rate ofthe aromatic alcohol over the catalyst (weighted hourly space velocityor WHSV) is from 0.01 to 100 grams per hour per gram (g/g·h). In someembodiments, WHSV is from 0.1 to 20 g/g·h, alternatively 0.1 to 5 g/g·h,or alternatively 0.1 to 1 g/g·h.

In some embodiments, it may be useful to subject the reactor to startupconditions which may provide various benefits, such as prolongingcatalyst life. Suitable startup condition include, for example, exposingthe catalyst to dilute amounts of the aromatic alcohol at lowertemperature before changing to full operating conditions as describedabove and demonstrated by the examples.

Following the reaction, the diaryl ether product is recovered from thecatalyst and optionally further purified. Unreacted alcohol and otherreaction by-products may be separated using methods known in the art.Such methods include but are not limited to distillation, crystalrefining, simulated moving bed technique or a combination thereof.

In some embodiments, the diaryl ether prepared by the process of theinvention is diphenyl oxide (DPO). Other diaryl ether compounds that maybe prepared by the process of the invention include, without limitation,compounds containing at least one ether functionality whereby two arylmoieties are connected by an oxygen atom (Ar—O—Ar′), including polyarylcompounds and compounds prepared from the aromatic alcohols describedabove. Specific examples include, but are not limited to, phenoxytolueneisomers, including 3-phenoxytoluene, ditolyl ether isomers, polyphenylethers (PPEs), biphenylphenyl ether isomers and naphthyl phenyl ethers.

The diaryl ethers prepared by the invention are useful in a variety ofapplications, including as high temperature solvents, as intermediatesin preparing flame retardants and surfactants, and as components in heattransfer fluids. Furthermore, certain diaryl ethers prepared by theinvention are useful as high performance lubricants and as intermediatesin preparing pyrethroid insecticides.

In some embodiments, a preferred use of the diaryl ether is in hightemperature heat transfer fluids. High temperature heat transfer fluidsmay be prepared by making the diaryl ether according to the processdescribed above and then mixing the diaryl ether with biphenyl. Theamounts necessary to provide a suitable fluid can be readily determinedby a person with ordinary skill in the art. For diphenyl oxide andbiphenyl, the amount of DPO may be, for instance, from 70 to 75 weightpercent based on the total weight of the DPO and biphenyl. A preferredamount of DPO is that required to form a eutectic mixture with thebiphenyl, which is about 73.5 weight percent based on the total weightof the DPO and biphenyl.

Some embodiments of the invention will now be described in detail in thefollowing Examples.

EXAMPLES Example 1

Holmium(III) oxide is used for the conversion of phenol to diphenyloxide (DPO). The powder is pressed and sieved to obtain particles thatare between 0.60 mm and 0.85 mm in diameter. The particles are loadedinto an electrically heated stainless steel reactor tube and heated tothe reaction temperature with nitrogen flowing through the tube. Afterthe reaction temperature is reached, vapor-phase phenol is passedthrough the reactor tube. The conversion of phenol is carried out at aweighted hourly space velocities of 1 (WHSV=gram phenol/gramcatalyst-hour) and at 500° C. Test conditions and results are shown inTable 1.

TABLE 1 Conversion Selectivity [mol. %] [mol. %] Diphenyl TestConditions phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.0.11% 48.63% 0.90% 50.47% 0.00% 0.00% 0.00% Feed: 33% PhOH, 67% N2 ToS =1 hrs WHSV 1 hr⁻¹ T = 500° C. 0.09% 48.97% 0.56% 50.47% 0.00% 0.00%0.00% Feed: 33% PhOH, 67% N2 ToS = 2 hrs WHSV 1 hr⁻¹ T = 500° C. 0.06%51.51% 0.20% 48.29% 0.00% 0.00% 0.00% Feed: 33% PhOH, 67% N2 ToS = 5 hrsWHSV 1 hr⁻¹ OPP: orthophenylphenol DBF: dibenzofuran O-BIPPE:ortho-biphenylphenyl ether M-BIPPE: meta-biphenylphenyl ether P-BIPPE:para-biphenylphenyl ether PhOH: phenol N2: nitrogen ToS: time on stream(ToS = 0 hours defined at start of phenol flow)

Example 2

The synthesis of the chlorided holmium oxide (Cl—Ho₂O₃) is carried outby a thermal decomposition of HoCl₃.6 H₂O. Thus, a sample of thepowdered precursor (approximately 10 g) is calcined in air in a staticcalcination oven under the following temperature protocol: ramp 1.41°C./min to 550° C., dwell 3 hours at 550° C., cool down to roomtemperature. The chlorine content of the catalyst is assayed by XRF to13.58 wt. % chlorine. The XRD data showed the presence of holmiumoxychloride phases.

The catalyst is used in the dehydration of phenol. The powder is pressedand sieved to obtain particles that are between 0.60 mm and 0.85 mm indiameter. The particles are loaded into an electrically heated stainlesssteel reactor tube and heated to the reaction temperature with nitrogenflowing through the tube. After the reaction temperature is reached,vapor-phase phenol is passed through the reactor tube. The conversion ofphenol is carried out at a weighted hourly space velocities of 1(WHSV=gram phenol/gram catalyst·hour) and at 500° C. Test conditions andresults are shown in Table 2.

TABLE 2 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.1.23% 92.68% 0.31%  7.01% 0.00% 0.00% 0.00% Feed: PhOH ToS = 2.25 hrsWHSV 1 hr⁻¹ T = 500° C. 1.36% 91.33% 0.31%  8.37% 0.00% 0.00% 0.00%Feed: PhOH ToS = 3.25 hrs WHSV 1 hr⁻¹ T = 500° C. 1.57% 88.91% 0.17%10.91% 0.00% 0.00% 0.00% Feed: PhOH ToS = 4.25 hrs WHSV 1 hr⁻¹ T = 500°C. 1.45% 87.46% 0.40% 12.14% 0.00% 0.00% 0.00% Feed: PhOH ToS = 5.5 hrsWHSV 1 hr⁻¹

Example 3

A 1M DyCl₃ solution, prepared by dissolving 18.849 g DyCl₃ in 50 mL DIH₂O, is added dropwise along with tetrapropylammonium hydroxide (76.261g, from a 40 wt % TPAOH solution) over 15 min into a 600 mL beakercontaining an initial 100 mL DI H₂O. The solution is stirred at 500 rpmon magnetic stir plate with a 3 inch stir bar. The resulting precipitateis allowed to age in solution for 1 h with stirring, after which it iscentrifuged at 5000 rpm for 10 min. The decanted precipitate is placedinto an oven, dried at 120° C. for 4 h and calcined at 500° C. for 4 hwith a ramp rate of 5° C./min to yield 8.6 g of product.

Example 4

Catalytic evaluation of the catalyst from Example 3 is carried out usinga similar procedure as in Example 2. Test conditions and results areshown in Table 3.

TABLE 3 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C. 8.30% 96.11% 0.01% 3.61% 0.00% 0.14% 0.14% Feed: PhOH ToS = 1.25 hrsWHSV 1 hr⁻¹ T = 500° C. 11.74% 97.58% 0.10% 2.14% 0.00% 0.08% 0.09%Feed: PhOH ToS = 2.25 hrs WHSV 1 hr⁻¹ T = 500° C.  6.36% 96.68% 0.25%2.79% 0.00% 0.11% 0.16% Feed: PhOH ToS = 3.75 hrs WHSV 1 hr⁻¹ T = 500°C. 11.88% 95.96% 0.10% 3.63% 0.04% 0.09% 0.19% Feed: PhOH ToS = 4.75 hrsWHSV 1 hr⁻¹

Example 5

A 1M YbCl₃ solution, prepared by dissolving 19.387 g YbCl₃ in 50 mL DIH₂O, is added dropwise along with tetrapropylammonium hydroxide (76.265g, from a 40 wt % TPAOH solution) over 15 min into a 600 mL beakercontaining an initial 100 mL DI H₂O. The solution is stirred at 500 rpmon magnetic stir plate with a 3 inch stir bar. The resulting precipitateis allowed to age in solution for 1 h with stirring, after which it iscentrifuged at 5000 rpm for 10 min. The decanted precipitate is placedinto an oven, dried at 120° C. for 4 h and calcined at 500° C. for 4 hwith a ramp rate of 5° C./min to yield 9 g of product.

Example 6

Catalytic evaluation of the catalyst from Example 5 is carried out usinga similar procedure as in Example 2. Test conditions and results areshown in Table 4.

TABLE 4 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.19.76% 97.39% 0.15% 2.18% 0.02% 0.19% 0.07% Feed: PhOH ToS = 1.5 hrsWHSV 1 hr⁻¹ T = 500° C. 22.20% 97.53% 0.06% 2.20% 0.02% 0.14% 0.06%Feed: PhOH ToS = 2.5 hrs WHSV 1 hr⁻¹ T = 500° C. 22.29% 97.55% 0.10%2.10% 0.04% 0.14% 0.06% Feed: PhOH ToS = 3 hrs WHSV 1 hr⁻¹

Example 7

A 1M ErCl₃ solution, prepared by dissolving 15.272 g ErCl₃ in 40 mL DIH₂O, is added dropwise along with tetrapropylammonium hydroxide (61.030g, from a 40 wt % TPAOH solution) over 15 min into a 600 mL beakercontaining an initial 100 mL DI H₂O. The solution is stirred at 500 rpmon magnetic stir plate with a 3 inch stir bar. The resulting precipitateis allowed to age in solution for 1 h with stirring, after which it iscentrifuged at 5000 rpm for 10 min. The decanted precipitate is placedinto an oven, dried at 120° C. for 4 h and calcined at 500° C. for 4 hwith a ramp rate of 5° C./min to yield 7.4 g of product.

Example 8

Catalytic evaluation of the catalyst from Example 7 is carried out usinga similar procedure as in Example 2. Test conditions and results areshown in Table 5.

TABLE 5 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.23.67% 97.71% 0.14% 1.99% 0.02% 0.10% 0.04% Feed: PhOH ToS = 4.5 hrsWHSV 1 hr⁻¹ T = 500° C. 22.86% 97.75% 0.18% 1.85% 0.01% 0.15% 0.06%Feed: PhOH ToS = 5.5 hrs WHSV 1 hr⁻¹

Example 9

A 1M HoCl₃ solution, prepared by dissolving 11.388 g HoCl₃ in 30 mL DIH₂O, is added dropwise along with tetrapropylammonium hydroxide (45.759g, from a 40 wt % TPAOH solution) over 15 min into a 600 mL beakercontaining an initial 100 mL DI H₂O. The solution is stirred at 500 rpmon magnetic stir plate with a 3 inch stir bar. The resulting precipitateis allowed to age in solution for 1 h with stirring, after which it iscentrifuged at 5000 rpm for 10 min. The decanted precipitate is placedinto an oven, dried at 120° C. for 4 h and calcined at 500° C. for 4 hwith a ramp rate of 5° C./min to yield 5 g of product.

Example 10

Catalytic evaluation of the catalyst from Example 9 is carried out usinga similar procedure as in Example 2. Test conditions and results areshown in Table 6.

TABLE 6 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.12.22% 97.77% 0.21% 1.87% 0.02% 0.07% 0.07% Feed: PhOH ToS = 1.75 hrsWHSV 1 hr⁻¹ T = 500° C. 12.73% 97.90% 0.28% 1.63% 0.00% 0.13% 0.07%Feed: PhOH ToS = 3.75 hrs WHSV 1 hr⁻¹ T = 500° C. 12.34% 97.95% 0.24%1.61% 0.02% 0.11% 0.05% Feed: PhOH ToS = 5 hrs WHSV 1 hr⁻¹ T = 500° C.12.02% 97.88% 0.12% 1.82% 0.00% 0.11% 0.07% Feed: PhOH ToS = 7 hrs WHSV1 hr⁻¹

Example 11

The synthesis of supported holmium oxychloride is carried out via anincipient wetness impregnation of gamma alumina.

Precursors:

Support: gamma alumina (Saint-Gobain NorPro, 30-60 mesh size, BET=178.9m²/g) that exhibits an incipient wetness condition of approximately 0.75mL per 1 g. Solution: holmium(III) chloride hexahydrate (HoCl₃.6 H₂O)and deionized water (DI water), prepared to c=0.7500 mol/L

Synthesis:

3.75 mL of the solution is added dropwise to 5 g of the support atambient conditions under vigorous shaking using a shaker plate. Theimpregnated material is then dried at 150° C. for 1 h, and theimpregnation procedure is repeated three more times (total of 4×3.75 mLused for 5 g of carrier) to achieve a high loading of holmium inside thepores of the carrier. The preparation is finished off by calcining theimpregnated material in a static air calcination oven using thefollowing protocol: ramp 1° C./min; dwell at T=550° C. for 3 hrs, cooldown to room temperature. The chlorine content of the catalyst isassayed by XRF to 4.48 wt. % chlorine.

Example 12

Catalytic evaluation of the catalyst from Example 11 is carried outusing a similar procedure as in Example 2. Test conditions and resultsare shown in Table 7.

TABLE 7 Conversion Selectivity [mol. %] [mol. %] Diphenyl TestConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.4.57% 82.05% 2.32% 15.22% 0.06% 0.17% 0.19% Feed: PhOH ToS = 1.25 hrsWHSV 1 hr⁻¹ T = 500° C. 4.05% 83.70% 1.21% 14.45% 0.08% 0.17% 0.39%Feed: PhOH ToS = 2.25 hrs WHSV 1 hr⁻¹ T = 500° C. 4.03% 84.56% 2.16%12.35% 0.08% 0.15% 0.70% Feed: PhOH ToS = 3.5 hrs WHSV 1 hr⁻¹ T = 500°C. 3.20% 86.04% 2.86% 10.42% 0.09% 0.00% 0.58% Feed: PhOH ToS = 4.25 hrsWHSV 1 hr⁻¹

Example 13

The synthesis of supported holmium oxychloride is carried out via anincipient wetness impregnation of amorphous silica.

Precursors:

Support: amorphous silica (WR Grace-Davison 57, 30-60 mesh size,BET=275.3 m²/g) that exhibits an incipient wetness condition ofapproximately 0.90 mL per 1 g. Solution: holmium(III) chloridehexahydrate (HoCl₃.6 H₂O) and deionized water (DI water), prepared toc=1.25 mol/L.

Synthesis:

4.5 mL of the solution is added dropwise to 5 g of the support atambient conditions under vigorous shaking using a shaker plate. Theimpregnated material is then dried at 150° C. for 1 h, and thepreparation is finished off by calcining the impregnated material in astatic air calcination oven using the following protocol: ramp 1°C./min; dwell at T=550° C. for 3 hrs, step down to room temperature. Thechlorine content of the catalyst is assayed by XRF to 2.02 wt. %chlorine.

Example 14

Catalytic evaluation of the catalyst from Example 13 is carried outusing a similar procedure as in Example 2. Test conditions and resultsare shown in Table 8.

TABLE 8 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.1.91% 53.78% 0.24% 45.76% 0.00% 0.00% 0.22% Feed: PhOH ToS = 1.5 hrsWHSV 1 hr⁻¹ T = 500° C. 1.86% 52.16% 4.21% 43.27% 0.00% 0.00% 0.36%Feed: PhOH ToS = 2.25 hrs WHSV 1 hr⁻¹ T = 500° C. 1.49% 52.09% 7.17%40.36% 0.00% 0.00% 0.39% Feed: PhOH ToS = 3 hrs WHSV 1 hr⁻¹ T = 500° C.1.50% 51.08% 1.44% 47.09% 0.00% 0.00% 0.39% Feed: PhOH ToS = 3.75 hrsWHSV 1 hr⁻¹

Example 15

A preparation of a holmium oxychloride sample is accomplished by settingup a 2-L 3-necked flask with two air-tight addition funnels, pH meter,and argon bubbling into 750 ml of DI H₂O at a flow rate of 300 sccm.After purging with argon, an aqueous solution of HoCl₃, prepared bydissolving 62.6 g HoCl₃ in 165 mL DI H₂O, is added dropwise over 0.5hours along with a controlled addition of aqueous ammonia to maintainthe pH constant at 9. The resulting suspension is added to a nitrogenpurged centrifuge container, capped, and centrifuged to separate theprecipitate from the solution. The liquid is poured off and thecontainers are placed in a vacuum oven at 80° C. for 16 hours. The driedsample is transferred into a purged quartz tube within a tube furnacewhere it is treated in flowing 1% oxygen in helium mixture for 5 minutesat room temperature, thermally treated at 500° C. for 3 h, and thencooled to room temperature in flowing nitrogen.

Example 16

Catalytic evaluation of the catalyst from Example 15 is carried outusing a similar procedure as in Example 2. Test conditions and resultsare shown in Table 9.

TABLE 9 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.17.92% 96.73% 0.58% 2.53% 0.01% 0.14% 0.00% Feed: PhOH ToS = 1.5 hrsWHSV 1 hr⁻¹ T = 500° C. 14.96% 96.44% 0.36% 3.01% 0.02% 0.17% 0.00%Feed: PhOH ToS = 2.5 hrs WHSV 1 hr⁻¹ T = 500° C. 12.90% 96.34% 0.66%2.91% 0.02% 0.05% 0.02% Feed: PhOH ToS = 3.75 hrs WHSV 1 hr⁻¹ T = 500°C. 11.21% 96.15% 0.84% 2.88% 0.00% 0.09% 0.05% Feed: PhOH ToS = 4.75 hrsWHSV 1 hr⁻¹

Example 17

Preparation of 16 wt % Ho supported on ZrO₂ via incipient wetnessimpregnation.

Prior to the impregnation process a hydrous ZrO₂ support with BETsurface area of 323 m²/g is pre-dried at 120° C. for 4 hours in staticair. 16 wt % Ho on ZrO₂ catalyst is prepared by two step incipientwetness impregnation of the treated ZrO₂ at ambient temperature. A glassbeaker is charged with 5 g of pre-dried ZrO₂. A 10-ml graduated cylinderis loaded with 0.9207 g of HoCl₃.6H₂O to yield 8 wt % of Ho and with 1.2ml of H₂O. The support is impregnated with aqueous solution of holmiumbeing added to the ZrO₂ in small fractions. After each addition, thesupport is agitated to break up clumps and uniformly disperse holmiumthroughout the carrier material. After the first step impregnation, thesample is dried at 110° C. for 4 hours. In the next step the wholeprocess is repeated using 0.9159 g of HoCl₃.6H₂O to again yield 8 wt %of Ho with 1.2 ml of H₂O. The impregnated sample is then treated at 110°C. for 4 hours in flowing air and then at 600° C. for an additional 4hours a 5° C./min ramp.

Example 18

Catalytic evaluation of the catalyst from Example 17 is carried outusing a similar procedure as in Example 2. Test conditions and resultsare shown in Table 10.

TABLE 10 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.2.73% 93.82% 0.05%  6.13% 0.00% 0.00% 0.00% Feed: PhOH ToS = 1 hr WHSV 1hr⁻¹ T = 500° C. 5.59% 86.86% 1.73% 11.42% 0.00% 0.00% 0.00% Feed: PhOHToS = 2.75 hrs WHSV 1 hr⁻¹ T = 500° C. 4.01% 84.15% 3.12% 12.72% 0.00%0.00% 0.00% Feed: PhOH ToS = 4 hrs WHSV 1 hr⁻¹ T = 500° C. 3.28% 83.79%1.37% 14.84% 0.00% 0.00% 0.00% Feed: PhOH ToS = 5 hrs WHSV 1 hr⁻¹

Example 19 Preparation of 15 wt % Yb Supported on ZrO₂ Via IncipientWetness Impregnation

Synthesis:

Prior to the impregnation process a hydrous ZrO₂ support with BETsurface area of 323 m²/g is pre-dried at 120° C. for 4 hours in staticair. 15 wt % Yb on ZrO₂ catalyst is prepared by two step incipientwetness impregnation of the treated ZrO₂ at ambient temperature. A glassbeaker is charged with 5 g of pre-dried ZrO₂. A 10-ml graduated cylinderis loaded with a 0.8405 g of YbCl₃.6H₂O to yield 7.5 wt % of Yb and with1.2 ml of H₂O. The support is impregnated with aqueous solution ofytterbium being added to the ZrO₂ in small fractions. After eachaddition, the support is agitated to break up clumps and uniformlydisperse ytterbium throughout the carrier material. After the first stepimpregnation, the sample is dried at 110° C. for 4 hours. In the nextstep the whole process is repeated using 0.8370 g of YbCl₃.6H₂O to againyield 7.5 wt % of Yb with 1.2 ml of H₂O. The impregnated sample is thentreated at 110° C. for 4 hours in flowing air and then at 600° C. for anadditional 4 hours at 5° C./min ramp.

Example 20

Catalytic evaluation of the catalyst from Example 19 is carried outusing a similar procedure as in Example 2. Test conditions and resultsare shown in Table 11.

TABLE 11 Conversion Selectivity [mol. %] Test [mol. %] DiphenylConditions Phenol Oxide OPP DBF O-BIPPE M-BIPPE P-BIPPE T = 500° C.6.05% 71.96% 6.61% 20.74% 0.06% 0.64% 0.00% Feed: PhOH ToS = 1 hr WHSV 1hr⁻¹ T = 500° C. 4.08% 73.59% 6.35% 17.09% 0.00% 0.99% 1.98% Feed: PhOHToS = 2.75 hrs WHSV 1 hr⁻¹ T = 500° C. 4.03% 71.42% 4.67% 21.49% 0.00%0.72% 1.69% Feed: PhOH ToS = 4 hrs WHSV 1 hr⁻¹ T = 500° C. 2.97% 73.63%5.57% 17.87% 0.00% 0.78% 2.15% Feed: PhOH ToS = 5 hrs WHSV 1 hr⁻¹

We claim:
 1. A method for preparing a diaryl ether, the methodcomprising dehydrating an aromatic alcohol compound over a dehydrationcatalyst, wherein the dehydration catalyst is an oxide of a heavy rareearth element.
 2. The method of claim 1 wherein the dehydration catalystfurther comprises a halogen.
 3. The method of claim 2 wherein thehalogen is chloride or fluoride ion.
 4. The method of any one of claims1-3 wherein the dehydration catalyst further comprises a binder.
 5. Themethod of any one of claims 1-4 wherein the dehydration catalyst issupported.
 6. The method of any one of claims 1-4 wherein thedehydration catalyst is unsupported.
 7. The method of any one of claims1-6 wherein the dehydration of the alcohol is conducted at a temperaturefrom 250 to 600° C.
 8. The method of any one of claims 1-7 wherein thealcohol feed is diluted with a diluent.
 9. The method of any one ofclaims 1-8 wherein the aromatic alcohol compound is phenol and thediaryl ether produced is diphenyl oxide.
 10. A method for producing aheat transfer fluid, the method comprising: preparing a diaryl ether bycontacting an aromatic alcohol compound with a dehydration catalyst,wherein the dehydration catalyst is an oxide of a heavy rare earthelement; isolating the diaryl ether from the dehydration catalyst; andmixing the isolated diaryl ether with biphenyl, wherein the mixtureforms a eutectic mixture.